This invention relates in general to a method of treating waste material and in particular to a new and useful method of biologically drying waste material in order to obtain soil conditioners, and of utilizing the internal energy thereof, while at the same time reducing the volume of the waste material, and in which composts of a refuse-sewage sludge mixture are subjected to intense rotting whereby the water content thereof is reduced from an initial value of 50 to 60 percent to about 30 percent, and preferably 20 percent.
Both the growing occurrence of refuse of various nature and source and the increasing awareness among the population of the importance of environmental conditions help to realize what limits are set to the prior art methods of refuse disposal. These limits may particularly clearly be illustrated by the situation of refuse deposits: dumps are the simplest and insofar also the cheapest way of refuse disposal. In view of the necessary complying with regulations and other restrictions intended to protect people, animals, and the environment in general, it becomes noticeably more difficult for operators, for example, communities, to maintain such dumps. This means that the suitable deposit areas provided therefor become scarce. The distances between dumps and the settlement areas to be serviced also become larger. Similar criteria are to be applied to the costs of environmental protection, such as to avoid contamination of ground water, if additional or future damages are to be prevented.
Aside from the fact that dumps attract vermin and may become centers of epidemics, putrefaction may cause methane explosions etc. resulting in dump fires. Further, by dumping of refuse, variable unsorted raw materials get lost instead of being recycled in a useful and appropriate manner.
Certain natural limits are also set to composting refuse and refuse-sludge mixtures, even though composting methods have proved to be practical. One such very successful method is disclosed in German patent No. 11 45 646. According to this method referenced above, soil conditioners from refuse which are unaffected by storing and which are substantially odorless and biologically active can be produced by preparing and drying mixtures of refuse and sludge. This method is called "intense rotting" notwithstanding the fact that a lot of degradable, organic material remains undegraded by this known method.
While applying the method of the above cited German patent, a mixture of partly dehydrated sludge and comminuted refuse is compacted under strong pressure to about a third of its initial volume without water expulsion. The compacts thus obtained are then airdried. The substantially odorless material obtained is suitable as a biologically active substance for conditioning the soil, i.e., for initiating the composting process or continuous fermentation processes in the soil, as a biological fuel, for example for heating horticultural compost heaps, for superficial composting, heating hotbed frames (substitute for horse dung), for mulching, eliminating development of bad odors upon using fecal matter, in boneyards, etc., and can be employed as a soil conditioner (to mellow the soil) particularly in instances where the cultivation is endangered by de-humification, since it converts all the raw organic matter in the soil into humus, i.e., starts the natural process of humification. Due to the concentration of organic matter, in briquet form, the briquets have a calorific value of 1,700 to 2,000 kcal/kg and, should later their production exceed their need as conditioner, are such that they can readily and with a better efficiency be burned, without requiring special furnaces, thus at substantially lower costs as compared to the conventional, very expensive waste incineration. However, having reference to the size of the briquets (f. i. 5'.times.7.5'.times.8.2') a complete combustion is not to be experted in view of the short stay time in the furnace.